A conventional switch device receives power from a power source, and is switchable between outputting and not outputting the received power to a load. A conventional transfer switch system includes a plurality of such conventional switch devices, each of which receives power from a respective power source. These conventional switch devices are controlled in such a way that one of the conventional switch devices outputs the power received thereby to power a load. When a primary one of the power sources (e.g., a grid power source) that currently powers the load through the conventional transfer switch system becomes abnormal (e.g., when a brownout condition or a dropout condition is encountered), the conventional transfer switch system is controlled such that a backup one of the power sources (e.g., an uninterruptible power supply) powers the load through the conventional transfer switch system instead.
For the conventional transfer switch system, each conventional switch device induces a relatively large transient current when switching between outputting and not outputting the received power to the load. Under a circumstance where each conventional switch device includes a relay, electrical contacts of the relay are easily welded to each other due to the relatively large transient current, and as a result, the conventional switch device cannot operate normally and thus has poor reliability.